Method of forming backside illuminated image sensor device with shielding layer

ABSTRACT

A backside illuminated image sensor device with a shielding layer and a manufacturing method thereof are provided. In the backside illuminated image senor device, a patterned conductive shielding layer is formed on a dielectric layer on a backside surface of a semiconductor substrate and surrounding a pixel array on a front side surface of the semiconductor substrate.

CROSS-REFERENCES TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 14/073,580 filed Nov. 6, 2013, now U.S. Pat. No. 11,335,721,issued on May 17, 2022, which is incorporated herein in its entirety.

BACKGROUND Technical Field

The disclosure generally relates to image sensors, especially CMOS imagesensors.

Description of Related Art

An image sensor provides an array of pixels for recording an intensityor brightness of light. The pixel responds to the light by accumulatinga charge. The more light is received, the higher the charge isaccumulated. The charge can then be used by another circuit so thatinformation of color and brightness can be used for a suitableapplication, such as a digital camera. Common types of pixels include acharge-coupled device (CCD) or complementary metal oxide semiconductor(CMOS) image sensor.

Comparing with conventional front-side illuminated (FSI) sensor,backside illuminated (BSI) sensor has been applied on CMOS image sensorto improve the sensitivity of each pixel in the CMOS image sensor. ForCMOS image sensor using backside illumination technology, pixels arelocated on a front side of a substrate, and the substrate is thinnedenough to allow light projected on the backside of the substrate toreach the pixels.

However, during the manufacturing process of the BSI sensor,electrostatic charges are often accumulated, and the wafer used can beeasily damaged by the accumulated electrostatic charges in a form ofarcing to decrease the yield of the BSI sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are plane diagrams of a backside illuminated image sensordevice with a conductive shielding layer according to embodiments ofthis disclosure.

FIGS. 2A-2C are cross-sectional diagrams showing a manufacturing processof a backside illuminated image sensor device with a conductiveshielding layer in FIG. 1A.

FIG. 3 is a flow chart showing the manufacturing process of a backsideilluminated image sensor device with a conductive shielding layer inFIGS. 2A-2C.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the disclosed embodiments. It will be apparent,however, that one or more embodiments may be practiced without thesespecific details. In other instances, well-known structures and devicesare schematically shown in order to simplify the drawing.

In the process of manufacturing a backside illuminated image sensordevice, it is found that a step of developing a photoresist layer on adielectric layer can generate electrostatic charge accumulated on thedielectric layer. The accumulated electrostatic charge can inducedischarging later in any time to damage the pixel array under thedielectric layer. Accordingly, it is designed to form a conductiveshielding layer on the dielectric layer to shielding the structuresunder the conductive shielding layer from outer applied electric field,which may present in a plasma-assisted deposition step or in aplasma-assisted etching step. Then, the discharging behavior of theaccumulated electrostatic charges can be reduced or even be prevented.

In various embodiments, this disclosure provides a backside illuminatedimage sensor device with a conductive shielding layer for shielding thestructures under the conductive shielding layer from outer appliedelectric field. FIGS. 1A-1C are plane diagrams of a backside illuminatedimage sensor device with a conductive shielding layer according to someembodiments of this disclosure. A cross-sectional diagram of the cuttingline AA′ is shown in FIG. 2B.

In FIGS. 1A and 2B, a pixel array 110 is disposed on a front surface ofa wafer 100. The pixel array 110 includes photodiodes (not shown) in thesemiconductor substrate 100 and metal lines 104 in the interconnectlayer 102. A dielectric layer 120 is disposed on a back surface of thewafer 100 to cover the backside of the pixel array 110. A plurality ofscribe lines 130 are formed in the dielectric layer 120.

A conductive shielding line 140 a is disposed on the dielectric layer120. The conductive shielding line 140 a is located on an area betweenthe pixel array 110 and scribe lines 130 and fills the area. Therefore,the conductive shielding line 140 a does not stop light irradiating onthe pixel array 110 to maximize the light intensity received by thepixel array 110.

In FIG. 1B, the conductive shielding line 140 a in FIG. 1A is thinned tothe conductive shielding line 140 b. However, for maintaining theshielding effect, the line width of the conductive shielding line 140 bis at least 300 μm.

The conductive shielding line 140 a in FIG. 1A can be further patternedto any patterns as long as the distributed conductive shielding lines issurrounding the pixel array 110 to give protection to the pixel array110. The shape of the each individual conductive shielding lines viewedfrom a top direction can be circle, square, polygon, or strip. Still,the narrowest width of the each individual conductive shielding lines isat least 300 μm. For example, the conductive shielding line 140 a inFIG. 1A can be patterned to conductive shielding lines 140 c in a shapeof strip and conductive shielding lines 140 d in a shape of square inFIG. 1C.

According to an embodiment of this disclosure, the conductive shieldinglines 140 a to 140 d can be made from a conductive material, such as ametal, a conductive oxide, a conductive polymer, or graphene. The metalcan be AI, Cu, Ti, Mo, or a MoCr alloy. The conductive oxide can be AZO(ZnO: Al), GZO (ZnO: Ga), GAZO (ZnO: Ga, Al), ATO (SnO₂: Sb), FTO (SnO₂:F), or ITO (In₂O₃: Sn). The conductive polymer can bepoly(3,4-ethylenedioxythiophene) (PEDOT), polyanilines (PANI), orcorresponding intrinsically conducting polymers (ICPs).

According to another embodiment of this disclosure, the dielectric layeris made from a dielectric material having a dielectric constant higherthan or equal to the dielectric constant of silicon oxide. For example,the dielectric layer can be made from silicon oxide or silicon nitride.

According to another embodiment of this disclosure, the dielectricbuffer layer is made from a dielectric material, such as silicon oxide.

In other embodiments, this disclosure provides a method of manufacturinga backside illuminated image sensor device. The backside illuminatedimage sensor device with a conductive shielding layer in FIG. 1A istaken as an example. Therefore, FIGS. 2A-2C are cross-sectional diagramsshowing a manufacturing process of a backside illuminated image sensordevice with a conductive shielding layer in FIG. 1A. In addition, FIG. 3is a flow chart showing the manufacturing process of a backsideilluminated image sensor device with a conductive shielding layer inFIGS. 2A-2C. FIGS. 2A-2C and FIG. 3 are referred hereinafter at the sametime.

In FIG. 2A and step 310, the pixel array 110 is formed on the frontsurface of the semiconductor substrate 100. The pixel array 110 includesphotodiodes (not shown) in the semiconductor substrate 100 and metallines 104 in the interconnect layer 102.

In FIG. 2A and step 320, the backside of the substrate 100 is thenthinned to reduce the thickness of the substrate 100 to allow lightstrike the photodiodes in the substrate 100. Next in step 330, adielectric layer 120 is formed on the back surface of the substrate 100.

In FIG. 2A and step 340, scribe lines 130 are formed in the dielectriclayer 120 by patterning the dielectric layer 120. The method ofpatterning the dielectric layer 120 can be photolithography and etching.In the step of developing photoresist in the photolithography process,since photoresist and the dielectric layer both are electricallyinsulating material, friction between two insulating materials oftenproduces electrostatic charges to be accumulated. The accumulatedelectrostatic charges may damage the pixel array 110 if no prevention orprotection treatment is made.

In FIG. 2B and step 350, a conductive shielding line 140 a is formed onthe dielectric layer 120 to protect the structures under the conductiveshielding line 140 a from discharging damage. The conductive shieldingline 140 a can be formed by depositing a conductive shielding layer, andthen patterning the conductive shielding layer by a method such asphotolithography and etching processes. Since the light receivedintensity by the photodiodes is better to be maximized, the conductiveshielding layer 120 is better not cover the backside of the pixel array110. However, if the conductive shielding line 140 a is transparent tolight, the conductive shielding line 140 a may cover the backside of thepixel array 110 according to various embodiments of this disclosure.

In FIG. 2C and step 360, a dielectric buffer layer 150 is formed on theconductive shielding line 140 a and dielectric layer 120. Next in step370 and step 380, a color filter layer 160 and a microlens layer 170 aresequentially formed on the dielectric buffer layer 150. Finally, theeach individual backside illuminated image sensor is separated from eachother by cutting along the scribe lines 130.

According to another embodiment of this disclosure, the conductiveshielding lines 140 b in FIG. 1B or 140 c-140 d in FIG. 1C can be formedthrough different photomask used in the above step of patterning theconductive shielding layer. The other steps are the same as theabove-described process, and hence are omitted here.

Accordingly, since at least a conductive shielding line is located onthe dielectric layer, any outer applied electric field cannot induce thecharging effect of the electrostatic charges accumulated under theconductive shielding layer.

All the features disclosed in this specification (including anyaccompanying claims, abstract, and drawings) may be replaced byalternative features serving the same, equivalent or similar purpose,unless expressly stated otherwise. Thus, each feature disclosed is oneexample only of a generic series of equivalent or similar features.

What is claimed is:
 1. A method of manufacturing a backside illuminatedimage sensor device, the method comprising: forming a dielectric layeron a back surface of a semiconductor substrate, wherein thesemiconductor substrate has an pixel array formed on a front surface ofthe semiconductor substrate; patterning the dielectric layer to form aplurality of scribe lines surrounding the pixel array; forming aconductive shielding layer on the dielectric layer; patterning theconductive shielding layer to expose the scribe lines; forming adielectric buffer layer on the patterned conductive shielding layer andthe dielectric layer; forming a color filter layer on the dielectricbuffer layer; and forming a microlens layer on the color filter layer.2. The method of claim 1, wherein the conductive shielding layer ispatterned to expose the pixel array.
 3. The method of claim 1, whereinthe conductive shielding line is made from a metal, a conductive oxide,a conductive polymer, or graphene.
 4. The method of claim 1, wherein awidth of the patterned conductive shielding layer is at least 300 μm. 5.The method of claim 1, wherein the dielectric layer is made from adielectric material having a dielectric constant higher than or equal tothe dielectric constant of silicon oxide.
 6. The method of claim 1,wherein the dielectric layer is made from silicon oxide or siliconnitride.
 7. The method of claim 1, wherein the dielectric buffer layeris made from silicon oxide.
 8. The method of claim 1, wherein the pixelarray is void of the patterned conductive shielding layer.
 9. The methodof claim 1, wherein the patterned conductive shielding layer has fourseparate conductive shielding lines respectively at four corners of thepixel array.
 10. A method comprising: forming a pixel array on afront-side of a substrate; depositing a dielectric layer on a backsideof the substrate; etching scribe line regions in the dielectric layer;after etching the scribe line regions in the dielectric layer, formingone or more conductive shielding lines on the dielectric layer, the oneor more conductive shielding lines non-overlapping the pixel array; andforming a color filter layer overlapping the pixel array.
 11. The methodof claim 10, wherein the one or more conductive shielding lines includea shielding line having frame-shaped pattern from a top view.
 12. Themethod of claim 11, wherein from the top view, the pixel array has aquadrilateral pattern enclosed by the frame-shaped pattern of theshielding line.
 13. The method of claim 10, wherein from a top view, theone or more conductive shielding lines comprise four first conductiveshielding lines respectively at four corners of the pixel array.
 14. Themethod of claim 13, wherein from the top view, the one or moreconductive shielding lines comprise four second conductive shieldinglines alternately arranged with the first conductive shielding lines andhaving a different top-view shape than the first conductive shieldinglines.
 15. The method of claim 14, wherein the first conductiveshielding lines have square top-view patterns, and the second conductiveshielding lines have rectangular top-view patterns.
 16. A methodcomprising: forming a pixel array on a substrate; depositing adielectric layer on the substrate; patterning the dielectric layer toform scribe line regions in the dielectric layer; and forming one ormore conductive shielding lines on the dielectric layer, the one or moreconductive shielding lines each having an outermost side in vicinity ofa boundary of the scribe line regions and an innermost sidenon-overlapping the pixel array.
 17. The method of claim 16, whereinforming the one or more conductive lines comprises: depositing aconductive shielding layer on the dielectric layer before patterning thedielectric layer to form the scribe line regions; and patterning theconductive shielding layer to form the one or more conductive shieldinglines.
 18. The method of claim 16, wherein the one or more conductiveshielding lines comprises a conductive shielding line having aframe-shaped top view.
 19. The method of claim 16, wherein the one ormore conductive shielding lines comprise four first conductive shieldinglines respectively at four corners of the pixel array.
 20. The method ofclaim 19, wherein the one or more conductive shielding lines comprisefour second conductive shielding lines alternately arranged with thefirst conductive shielding lines, and the second conductive shieldinglines each have a smaller width than the first conductive shieldinglines.